Cooling apparatus for cathode getter pumps



iuiy 38, 1967 R. L. JEPSEN 3,331,975

COOLING APPARATUS FOR CATHODT GETTBR PUMPS Filed Feb. 19, 1965 INVENTOR.

ROBERT L. JEPSEN Y MM United States Patent 3,331,975 COOLING APPARATUS FOR CATHODE GETTER PUMPS Robert L. .Iepsen, Los Altos, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Feb. 19, 1965, Ser. N 433,992 6 Claims. (Cl. 313-7) The present invention relates generally to glow discharge apparatus and particularly to sputter-iron pumps having greatly enhanced through-put capacity.

In my US. Patent No. 3,149,774 issued Sept. 22, 1964, there is disclosed a glow discharge apparatus including means for cooling the apparatus. In one specific embodiment of this patent the cooling means comprises an elongated heat conductive tubular member through which a cooling fluid may be circulated, brazed to the edges of the cathode plates on the surfaces facing the anode. This particular embodiment of the invention is widely used for evacuation during processing of the electronic tubes such as klystrons, magnetrons and traveling wave tubes where there is high out-gassing, for example, during the initial stages of the tube bake-out cycle and during activation of oxide-coated cathodes.

Where maximum through-put capacity is of prime importance apparatus of the type disclosed in the abovementioned patent is far superior to its uncooled counterpart. Nevertheless, recent experiments and operating experience have indicated that the cooled apparatus often does not perform as the earlier experience had indicated. The reason for this is associated with the effect of pumping hydrogen, as discussed below.

It is the principal object of the present invention to provide a glow discharge apparatus having improved high throughput capacity under the conditions often encountered in typical applications.

Briefly stated, in accordance with one teaching of the present invention there is disclosed a glow discharge apparatus having an anode electrode, a pair of cathode electrodes, usually made of titanium, spaced from the anode electrode and having portions disposed opposite the anode electrode and means adapted to cool the cathode electrodes in intimate contact with the portions disposed opposite the anode electrode. The cooling means may be an elongated heat conductive tubular member for circulating a cooling fluid and in those apparatuses which utilize an anode electrode having a plurality of openings therein defining a plurality of glow discharge passageways grouped transversely to the longitudinal axes of the passageways, the tubular member may either be intersected by or spaced from the axes of the glow discharge passageways.

It has been observed that at maximum through-put the central regions of the cathodes run quite hot despite peripheral cooling. Temperatures as high as 900 C. at the centers of the'cathodes have been observed. A significant portion of the gas load in processing microwave tubes is hydrogen, which is pumped primarily by diffusion into the cathodes. Since hydrogen is released from the titanium cathodes in significant quantities at temperatures of only a few hundred degrees centigrade, this thermal release of previously pumped hydrogen leads to reduced net through-puts and degraded performance from those obtained previously. In earlier tests and evaluations, gases such as nitrogen and carbon dioxide were employed. It was not realized that the hydrogen gas load encountered in processing microwave tubes, for example, would be of significance.

In the cooling means of the above-mentioned patent, the distance between the cooling tubulations was approximately 3 inches. With inch thick titanium cathodes operated under maximum through-put conditions, the temperature in the central regions of the cathodes would rise to 900 C. or higher. To keep the maximum cathode temperature less than about 300 C. (to prevent significant re-evolution of previously pumped hydrogen), it is necessary to provide cooling tubulations which are more closely spaced, for example, approximately 1 inch apart rather than 3 inches.

Thus instead of placing the cooling means in intimate contact with the edges of the cathodes, as in the past, in the present invention cooling means, which may comprise an elongated heat conductive tubular member for circulating fluid, is placed in addition in intimate contact with the central portions of the cathode. Where a multiple cell anode is utilized the cooling means may be arrayed in a variety of ways on the cathode. In one array the cooling means pass beneath the anode cell centers, that is, intersected by the cell axes. Since power tends to concentrate at the centers of the cells, placing the cooling means directly beneath the cell centers should improve heat transfer and lead to lower cathode temperatures. In another array the cooling means are deliberately spaced away from the anode cell axes, for example, along the anode cell interstices. Cathode erosion is greater at the cell centers. Eventually the cathode may be pierced completely. If the cooling means is placed directly beneath the cell axes, the cooling means may eventually puncture, leading to catastrophic p ump failure and letting the pump and device being evacuated up to water. The choice between these two means of cooling will depend on the application. Where the lowest cathode temperatures are required, the cooling tubulations should pass beneath the anode cell centers. Where catastrophic pump failure must be avoided, the cooling tubulations should be spaced away from the anode cell axes.

One feature of the present invention is the provision in a glow discharge apparatus of an anode electrode, a cathode electrode spaced from the anode electrode and having portions disposed opposite the anode electrode and means adapted to cool the cathode in intimate contact with the portions disposed opposite the anode electrode.

Another feature of the present invention is the provision in a glow discharge apparatus of an anode elec trode having a plurality of openings therein defining a plurality of glow discharge passageways grouped transversely to the longitudinal axes of the passageways, a cathode electrode spaced from the anode electrode and having portions disposed opposite the glOW discharge passageways, means adapted to cool the cathode in intimate contact with the portions disposed opposite the glow discharge passageways and either intersected by or spaced from the axes of the glow discharge passageways.

These and other features and objects of the present invention and a further understanding may be had by referring to the following description and claims, taken in conjunction with the following drawing in which:

FIG. 1 is a plan view partly in cross-section of a novel glow discharge apparatus of the present invention;

FIG. 2 is a cross-section taken along the lines 22 of FIG. 1; and

FIG. 3 is a plan view similar to FIG. 1 of an alternate embodiment of the present invention.

Referring now to FIGS. 1 and 2 a cup-shaped member 11 is closed off at its flanged open end 12 by a closure plate 13 welded thereto thereby forming an evacuable envelope 14. A side wall 15 of envelope 14 is apertured to receive a hollow conduit 16 provided with a mounting flange 17 for communication with a structure to be evacuated (not shown).

A cellular anode 18 of, for example, stainless steel, is carried within envelope 14 upon the end of a conductive rod 19 which extends outwardly of envelope 14 through an'opening in closure plate 13. Rod 19 is insulated from and carried on closure plate 13 through the intermediary of a high voltage teed-through 20., The free end of rod 19 provides a terminal for applying a positive anode voltage, typically, 210 kv., with-respect to two substantially rectangular cathode plates 21,'for example, titanium. By way of example, in a typical embodiment, the anode has 12 cells, approximately 1 inch square and 1 inch long.

The cathode plates 21 are spaced apart at their corners from each other and from anode 18 by means of spacers 22. At the opposite end the cathode plates are mechanically locked in position substantially parallel to and spaced from anode 18 by means of insulators 23 brazed toanode studs 24 and supported from the side walls 15,

25 of envelope 14 by means of brackets 26 and associated pins 27. By way of example, in a typical embodiment the cathode plates are 4.75 inches long, 3.75 inches high, 0.125 inch thick and are spaced apart 1.625 inches.

A permanent magnet 28 having a pair of pole pieces 29 is positioned against clips 30 such that its magneticlines of flux, typically 1000 gauss thread through the individual cellular elements, of anode 18 and in substantial parallelism to the longitudinal axes thereof.

The novel cooling means 31 of the present invention includes a continuous, elongated heat conductive tubing such as titanium brazed to the portions of the titanium cathode plates 21 directly opposite cellular anode 18 on their surfaces facing away from anode 18, through the use of tube clips 33 and aluminum as the brazing material. The ends of tubing 32. extend out of envelope 14 through apertures in end plate 13 which are closed by brazing cups 34. In the=embodiment disclosed. in FIGS. 1 and 2 the tubing 32 provides a path for a cooling fluid such as water in intimate contact with the portions of the cathode plates normally subjected to impinging positive ions produced by the glow discharge through the anode and between the cathode plates. The tubing 32, however, in this embodiment is spaced from the individual anode cell axes which normally are the regions of most intense ion bombardment, lying along the anode cell interstices.

In operation the applied potential produces a region of intense electric field between the cellular anode 18 and cathode plates 21.'This 6l6CtllC,'fild, acting in combina-. tion with the magnetic field, produces a breakdown of gas Within the pump resulting in a glow discharge within the individual cellular anode compartments and between the cathode plates 21. The glow discharge results in positive ions being driven into the cathode plates 21 to produce dislodgment of reactive'cathode material which is thereby sputtered onto the nearby anode 18 to produce gettering of molecules in the gaseous state coming in contact therewith. In this manner the pressure within the envelope 14 and, therefore, structures communicating therewith, is reduced. During operation, a cooling fluid such as water is circulated through the tubing 32. This circulation of fluid permits dissipation of heat in a more efficient manner than heretofore known from the ion bombarded portions of the cathode plates 21.

Referring nowto FIG. 3 thereis shown anotherembodiment of the present invention. The apparatus of this embodiment is substantially the same as that of the apparatus shown in FIGS. 1 and 2 with the exception that the tubing 32 is intersected by the individual cell axes of the anode 18.

Since many changes can be made in the above apparatus and many apparently widely difierent embodiments of this invention can be made without departing fromthe scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Whatis claimed is:

1. A glow discharge apparatus comprising:

an anode electrode having a plurality of openings therein defining a plurality of glow discharge passageways arranged in a pattern and grouped, transversely to the longitudinal axes of said passageways;

a cathode electrode spacedfro-msaid anode electrode and having portions disposed opposite said glow discharge passageways;

an evacuable envelope enclosing said anode and cathode electrodes; and

means adapted to cool said cathode in intimate contact with said cathode portions disposed opposite said glow discharge passageways, said cooling means being formed in a non-linear shape whereby portions of the cooling means lie adjacent other portions of the cooling means, said adjacent portions being substantially spaced from each other,- and said shape of the cooling means being determined by saidpattern of the discharge passageways.

2. The apparatus according to claim :1 wherein said cooling means comprises anelongated heat conductive tubular member for circulating a cooling fluid.

3. The apparatusaccording to claim 2 wherein said tubular member passes substantially across the axes of said glow discharge passageways.

4. The apparatus according to claim 2 wherein said tubular member is spaced from the axes of said glow discharge, passageways.

5. The apparatus according to claim 4 including means for producing and directing a magnetic field axially of and within a plurality of said glow discharge passageways.

6. The apparatus according to claim 5 including means for applying a potential to said anode electrode positive with respect to said cathode electrode.

References Cited UNITED STATES PATENTS 7/1939 Gross et al 3l3-35 X 9/1964 Jepsen 3l37 X 

1. A GLOW DISCHARGE APPARATUS COMPRISING: AN ANODE ELECTRODE HAVING A PLURALITY OF OPENINGS THEREIN DEFINING A PLURALITY OF GLOW DISCHARGE PASSAGEWAYS ARRANGED IN A PATTERN AND GROUPED TRANSVERSELY TO THE LONGITUDINAL AXES OF SAID PASSAGEWAYS; A CATHODE ELECTRODE SPACED FROM SAID ANODE ELECTRODE AND HAVING PORTIONS DISPOSED OPPOSITE SAID GLOW DISCHARGE PASSAGEWAYS; AN EVACUABLE ENVELOPE ENCLOSING SAID ANODE AND CATHODE ELECTRODES; AND MEANS ADAPTED TO COOL SAID CATHODE IN INTIMATE CONTACT WITH SAID CATHODE PORTIONS DISPOSED OPPOSITE SAID GLOW DISCHARGE PASSAGEWAYS, SAID COOLING MEANS BEING FORMED IN A NON-LINEAR SHAPE WHEREBY PORTIONS OF THE COOLING MEANS LIE ADJACENT OTHER PORTIONS OF THE COOLING MEANS, SAID ADJACENT PORTIONS BEING SUBSTANTIALLY SPACED FROM EACH OTHER, AND SAID SHAPE OF THE COOLING MEANS BEING DETERMINED BY SAID PATTERN OF THE DISCHARGE PASSAGEWAYS. 